1. Technical Field
This invention relates generally to metal gaskets. More particularly, it relates to embossed metal gaskets made from high temperature alloys. Even more particularly, to embossed metal gaskets made from high temperature iron-nickel-chromium alloys operative at temperatures up to about 1000° F.
2. Related Art
It is well known to use embossed metal for moderate to high temperature gaskets of internal combustion engines, including both gasoline and diesel fueled engines. For example, 301 stainless steel gaskets fully hardened by cold reduction (301 FH SS) perform acceptably up to about 800° F., but loses its strength at temperatures above about 1000° F. where the embossments take a heat set and fail to fully recover to their operational sealing state in use, thereby losing their ability to effectively seal a joint. However, even at operating temperatures below 1000° F., the performance of 301 FH SS and other stainless steels such as 309 FH CR and 316Ti diminishes proportionately with increasing temperature, from room temperature up to about 1000° F., and generally at an increasing rate above 800° F., as illustrated in FIG. 3 which illustrates the recovered embossment height as a function of temperature. This stress relaxation is important because this gradual decrease in the properties, even at moderate temperatures from about 230-550° F., for a given gasket design may cause the gasket loading to be reduced to the point that sealing is compromised. Frequently, such a decrease in properties is addressed in the gasket design by the incorporation of additional gasket layers to obtain the required gasket height and sealing properties. This temperature effect and limitation of gaskets that are subject to it is exacerbated in sealing applications where the joint to be sealed experiences large thermal or dynamic mechanical movement, such as in joints that are exposed to vibration, particularly those which also experience large temperature variations. This is frequently the case in many joints where a flanged member is attached to a mating joint member, particularly another flanged joint member. In sealing applications associated with internal combustion engines, examples include joints for certain head gasket configurations, exhaust downpipe clamps, intake manifolds and turbocharger intercoolers.